Process for heat treating food product

ABSTRACT

Proteinaceous food product is heated by immersing the product in a liquid and maintaining the liquid at a controlled temperature within a range that treats the proteinaceous food product without substantial loss of functionality.

This is a Division application Ser. No. 08/640,746, now U.S. Pat. No.5,916,617 filed Jun. 28, 1996, which in turn is a National Stage ofPCT/US94/12790, filed Nov. 7, 1994, which in turn is aContinuation-in-Part of application Ser. No. 08/148,915, now U.S. Pat.No. 5,494,687, filed Nov. 5, 1993. The entire disclosures of the priorapplications are hereby incorporated by reference herein in theirentirety.

BACKGROUND OF THE INVENTION

This invention relates to a process for heat treating food product. Theprocess is advantageously used for pasteurizing and/or tenderizingproteinaceous food product.

Pasteurizing of proteinaceous food product can be carried out by heatingto destroy infectious organisms such as salmonella. Pasteurization maybe defined as heat treatment for the purpose of killing or inactivatingdisease-causing organisms. For example for milk, a minimum exposure forpasteurization is 62° C. for 30 minutes or 72° C. for 15 seconds. Thelatter exposure is called flash pasteurization. Complete sterilizationmay require ultra-high pasteurization such as treatment at 94° C. for 3seconds to 150° C. for 1 second to kill pathogenic bacteria andinactivate enzymes that cause deterioration and to provide forsatisfactory storage life.

Minimum food safety processing standards for various commodities havebeen promulgated and are enforced by the United States Department ofAgriculture (USDA). Pasteurization may be defined in accord with thestandards mandated by the USDA. The Nutrition Action Health Letterpublished by the Center For Science In The Public Interest (July/August1991 Edition, Vol. 18, No. 6, “Name Your (Food) Poison”) describesconcern with the growing number of cases of food poisoning due to foodinfections.

Many known processes for pasteurizing food are insufficient to assuresafety of some foods from infections or cannot be applied to some foodproducts. The “Name Your (Food) Poison” article reports that dairyproducts, eggs, poultry, red meat and seafood, in that order are themost common causes of food poisoning. Shell eggs are particularlydifficult to pasteurize because of their structure. The articleindicates that one of 10,000 eggs is contaminated with salmonellaenteritis.

U.S. Pat. No. 4,808,425 to Swartzel et al. teaches a method of“ultrapasteurizing” a liquid whole egg product”. The liquid whole eggproduct is passed as a continuous stream through a pasteurizingapparatus. The liquid whole egg product is heated to a predeterminedreal temperature by contacting the product with a heated surface. Thetotal thermal treatment received by the whole egg product is prescribedby an equivalent temperature and an equivalent time that are defined topasteurize the material but insufficient to cause coagulation (loss offunctionality) of product.

U.S. Pat. No. 5,290,583 to Reznik et al. relates to an electroheatingprocess for treating liquid egg. The process comprises the steps ofelectroheating the liquid egg with an AC electric current having afrequency effective to heat the liquid egg without electrolysis at arate to avoid detrimental coagulation (loss of functionality). Theliquid egg is held at a temperature sufficient to achievepasteurization.

Functionality or functional properties of eggs relate to the volume,structure, texture and keeping quality of baked products produced by theeggs. Functionality is defined herein as the capability of aproteinaceous food product to provide the properties of the product thathas not been treated by the process of the present invention. Loss offunctionality is determined by observing the loss of quality of the foodproduct. For example, spoilage or cooking is a loss of functionality ofmeat in a process designed for aging of meat without cooking.Coagulation is a loss of functionality of shell eggs duringpasteurization. Cooking and/or loss of taste or texture is a loss offunctionality of oysters that are to be eaten uncooked.

The extent to which functional properties of a proteinaceous foodproduct are affected by heating may be determined by testing theperformance of the product under conditions in which the damage isreadily observed. For example, functionality of eggs can be establishedby determining the quality of food products that depend upon the qualityof coagulation of the egg. Such food products may include custards andpie fillings and loaves or croquettes which depend upon the binding offood together that may be provided by the quality of egg coagulation.The functional properties may also include the elasticity of an eggprotein film or the emulsifying ability to disperse oil in the making ofmayonnaise and salad dressings. Functionality or functional propertiesof other food product are similarly established in terms of thecapability of the food product to perform intended purposes after heattreatment including retaining a “natural” taste and texture.

While heat treatment may be effective in pasteurizing proteinaceous foodproduct, heating at the same time may destroy some functionality orfunctional properties of the product. The present invention provides aprocess for heat treating proteinaceous food product that achieves adelicate balancing of effective heat treatment without destruction offunctionality or functional properties.

The heat treating process of the present invention also provides amethod of quick aging of meat by exposure to an elevated temperaturewithout decomposition of the food product by cooking. Aging a meat canbe carried out by storing pieces of meat in a refrigerated space for atime sufficient to permit natural enzymes to complete a tenderizingprocess. Enzymes in the meat continue to function post-mortem tocatalyze the hydrolysis of collagen and other proteins. The enzymesbreak down connective tissue so that the meat becomes tender andflavorful. After aging, the texture of the meat is more acceptable tothe consuming public.

During aging, the meat is generally refrigerated at a temperature ofabout 34° F. to suppress bacterial growth and at a relative humidity ofabout 80% to suppress mold growth. However at these conditions, the rateof enzymatic action is suppressed. An average of twenty-one days or moreis often required to obtain satisfactory tenderizing. Substantial spacein a refrigeration facility is required to store the meat for thisperiod of time.

Increasing the temperature used in the aging process acceleratesactivity of the enzymes for tenderizing meat. However, bacterialactivity is also increased. Slime growth, putrefaction and mold growthresult in spoilage and can cause a substantial loss of usable meat.Maintaining low humidity in the refrigerated space to retard mold growthtends to desiccate and discolor meat. The desiccated and discoloredparts must be trimmed. Additionally, low humidity causes shrinkage.

U.S. Pat. No. 2,713,002 to Williams proposes aging meat by storing acarcass in the presence of ultra-violet radiation. The carcass iswrapped in a combination of absorbent material with amoisture-vapor-permeable, pliable, extensile film. The meat is wrappedin the film and held under ultraviolet radiation for five, ten, fifteenor twenty days at between 30° F. to 40° F.; for five or ten day periodsat 47° F.; for two, three or five days at 60° F.; or for one or two daysat 70° F. The covered meat is initially chilled in a cooler at atemperature of about 30° to 45° F. A period of twenty-four toseventy-two hours is required to bring the meat to an initial chilltemperature for aging of about 30° F. to 35° F.

U.S. Pat. No. 3,445,240 to Bedrosian et al. discloses tenderizing meatby storage under specific controlled chilled conditions and for definiteperiods of time in an atmosphere containing controlled amounts of oxygenand carbon dioxide at a high humidity.

U.S. Pat. No. 3,552,297 to Williams relates to an apparatus for agingand flavoring meat at a temperature of around 65° F. to 75° F. Theapparatus includes a germicidal lamp and a timer motor for setting theaging process for a period of one to four days. The aging process isconducted in the presence of Thamnidium, an anti-bacteria agent. U.S.Pat. No. 3,663,233 to Keszler teaches a process of tenderizing andcooking meat products by pumping the beef with a liquid tenderizingagent. The beef is heated to a constant temperature and maintained atsuch temperature to allow tenderizing by the tenderizing agent. Thetemperature is then raised to cook the meat.

U.S. Pat. No. 3.961,090 to Weiner et al. teaches pumping an aqueoussolution into a piece of uncooked beef, vacuum sealing the beef in a bagand cooking the beef “to attain a maximum internal temperature of 131°to 140° F.”

U.S. Pat. No. 3,966,980 to McGuckian discloses a method of cooking foodsin vacuum packages in a thermostatically controlled hot water bathfollowed by quick chilling and storage at 28° F. to 32° F. The bath ismaintained in a range between 140° F. to 212° F. to cook the meat atleast to a “rare” state. The cooked food is thereafter quick chilled forstorage. A disclosed advantage of the process is that the meat may beenzymatically tenderized while it is being cooked.

U.S. Pat. No. 4,233,323 to Sway et al. discloses a tenderization processof exposing meat to ultraviolet rays of high intensity.

U.S. Pat. No. 4,346,650 to Zaitsu discloses a bath for sterilizing andcooking food. The process is a two-step process requiring sterilizationat about 105° C. (221° F.) to about 140° C. (284° F.). The bathsterilizes and cooks packaged foods.

U.S. Pat. No. 4,983,411 to Tanaka et al. relates to an apparatus usedfor ultraviolet sterilization and shrink film packaging food. In thepackaging step, the food is sprinkled with hot water.

A process of heat treating proteinaceous food product below a cookingtemperature by exposure to an elevated temperature is desirable forpasteurizing, aging or both pasteurizing and aging the food product.However, elevated temperatures for periods required to pasteurize foodmaterial or to age food material can cause decomposition, i.e., loss offunctionality or cooking. Elevated temperatures at shorter periods oftime may not accomplish pasteurization or aging or may stimulatebacteria growth causing spoilage.

SUMMARY OF THE INVENTION

The present invention relates to a process of heat treatingproteinaceous food product by immersing the product in a liquid bath andmaintaining the entire volume of the bath at a controlled temperaturewithin a range of ±2° F. The process heat treats the proteinaceous foodproduct without substantial loss of functionality. The process can beused to effectively pasteurize or tenderize or otherwise treatproteinaceous food product.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The process of the invention permits heat treating food product withinan abbreviated period of time to provide pasteurization, tenderizing orboth pasteurizing and tenderizing. The process comprises immersing thefood product in a liquid bath such as a water bath. The entire volume ofthe bath is maintained at a controlled temperature within a range thatpasteurizes the food product without destroying functionality or thathastens enzymatic tenderizing of a food product but does notsubstantially cook the meat.

The heat treatment process of the present invention is particularlyuseful for pasteurizing food product such as seafood (e.g., fin fish andshellfish such as oysters, claims, scallops, mussels, crabs) and shellegg among many others. Shell egg may present a particular problem ofinfection. One source of infection may arise from the fact that eggshells have numerous pores that permit the egg to breathe. Pore holesvary in size. When the egg is laid, the holes come in contact withinfections in the environment outside of the egg. Some of the infectionsmay be in the form of microbes that are of a size that fit through thepores. Inside the egg, the microbes are not uniformly spread but areretained in small patches on the inner shell membrane that has poresthat are smaller than the shell. Additionally, airborne microorganismsmay invade an egg as a contaminant during gas and vapor exchange.Additionally, eggs can be contaminated by a transovarian infection.

Swartzel et al. describes USDA standards for pasteurizing liquid eggs.The minimum times for temperature processing required by USDA standardsproduces liquid eggs that are safe to eat while at the same time anacceptable degree of functionality is retained. However, standards forshell eggs are not available because no reliable temperature techniquefor treating shell eggs is known. Shell eggs present a particularproblem of pasteurization because the shell egg is made up of diversematerials. An effective temperature treatment must expose all of theshell, the outer shell and egg membranes, the albumen layer or eggwhite, the chalaza, the vitelline membrane and the yolk to temperaturesfor times to adequately destroy the undesired organisms withoutdestroying functionality.

To achieve these objectives, the shell egg may be exposed to aprepasteurization temperature of 45° F. or higher followed by exposureto temperatures from about 125° F. to near, but less than, 140° F.Another processing technique includes first processing at an elevatedtemperature near to 140° F. followed by a lowering of temperature to aprocessing temperature at the lower end of the effective pasteurizationtemperature range.

If temperatures are significantly above 139° F., the egg shell may crackand whites may begin to coagulate before the yolk has been pasteurized.At temperatures below the specified minimum, salmonella and otherharmful microorganisms, including molds, bacteria and viruses, may notbe effectively destroyed.

Processing times at these temperatures required for meeting minimum USDArequirements for liquid eggs range from a minimum processing time ofabout 20 minutes to a processing time of 345 minutes. Preferredtemperatures include a range of 135° F. to 138 or 139° F. These time andtemperature relationships are effective for pasteurization processing ofwhole shell eggs once an adequate prepasteurizing processing temperatureis achieved within the center of the whole shell egg of between about38° F. to about 60° F. The average first preprocessing temperatureshould be lower than about 45° F. for whole shell eggs for consumerdistribution.

The time and temperature relationships for pasteurizing shell eggs aredetermined in respect to the following factors: (1) temperaturesattained by all material within the mass of the shell egg and the timefor pasteurizing of the material at that temperature; and the averagetime that each material is heated to assure that each material issubjected to the least minimum condition to effectively pasteurize; and(2) the combination of processing parameters that will retainfunctionality by avoiding or minimizing adverse changes in appearanceand performance while maximizing destruction of infections.

The following table provides temperature and real processing time (RPT)relationships for destruction of harmful microorganisms in shell eggs:

TABLE 1 Temperature RPT (minutes) 130° F. (54.4° C.) = 65 131° F. (55.0°C.) = 49 132° F. (55.6° C.) = 38 133° F. (56.1° C.) = 28 134° F. (56.7°C.) = 20 135° F. (57.2° C.) = 16 136° F. (57.8° C.) = 11 137° F. (57.8°C.) = 8 138° F. (58.9° C.) = 4.75 140° F. (60.0° C.) = 3.5

These relationships describe processing of whole shell eggs afterattaining required pasteurizing preprocessing temperature. The initialpreprocessing temperature is applied until the shell egg reaches atemperature equilibrium with the heat transfer medium. The relationshipsof Table 1 are applicable after this point has been reached. Theprocessing temperature is defined as an equilibrium temperature whereheat has been transferred through external portions of the shell egginto the center of the yolk so that the temperature at the yolk centerand at every other locus throughout the mass of the egg has reached anequilibrium with the process medium.

Treatment times include processing times (RPT) from Table 1 plus thetime required for the egg to reach the preprocessing temperature.Certain factors may effect the time required for an egg to reach theeffective process temperature,including egg size, the temperature of theegg before application of heating and the selected pasteurizationprocess temperature. It is important that all of the egg be held at anappropriate temperature for an appropriate time to ensure pasteurizationof entire egg and that this can be accomplished without simultaneouscooking or disruption of functionality of any portion of the egg.

In a preferred embodiment, the heat treatment is carried out in at leasttwo steps. The process comprises a first heat treating at a temperatureto provide an internal egg temperature to destroy infectous organismswithout substantial loss of functionality. The first heat treating isfollowed by a second heat treating at a lower temperature to achievepasteurization. The steps combine to advantageously pasteurize shell eggwithout loss of functionality.

Advantageously, the process of the invention permits aging (tenderizing)of meat within an abbreviated period of time in the absence of achemical tenderizing agent and preferably also in the absence of ananti-bacteria agent. The process comprises immersing the meat in aliquid bath such as a water bath. The entire volume of the bath ismaintained at a controlled temperature within a range that hastens theenzymatic tenderizing of the meat. The temperature is preferably below aminimum cooked temperature of the meat, preferably at a temperature thatkills bacteria in at least the initial stages of the process. The meatis held at the bath temperature during tenderization. The process ofthis invention permits the tenderized meat to be chilled, stored, and/ordistributed and later cooked for serving.

Cooking uses heat to substantially decompose and change fibers of meat.Cooking adds texture and flavor and prepares the meat for humanconsumption. The term minimum cooked temperature for a meat as usedherein is a minimum temperature that a meat attains in preparation ofthe meat for human consumption as cooked meat.

The process of the invention can be applied to the aging of differenttypes of meat, for example, beef, veal, pork, mutton, lamb or poultry,most preferably beef. Cooked temperatures for various meats are known.Typical minimum cooked temperatures for typical meats are as follows:rare beef—140° F.; veal—175° F.; lamb—160° F.; pork 175° F.; poultry160° F. Thus suitable temperatures below the minimum cooked temperatureof the meat for use in the present invention include temperatures lessthan or equal to 133° F., such as 130° F., 125° F. or 120° F. for beef.For other meats, the tenderizing temperature is kept under 160° F.,preferably under 150° F. or 145° F., to avoid inactivation of enzymes.

Various sizes of meat can be tenderized by the process of the presentinvention. For example, very large sizes such as carcasses, primal cutsand whole muscle meat as well as various smaller sizes of meats can betenderized by the process of the invention. Suitable periods of time forconducting the process of the invention to obtain tenderizing of meatwill vary with the type of the meat once the meat has reached a uniformtemperature. In general, the meat should be maintained in the bath longenough to reach a uniform temperature throughout its thickness, and longenough thereafter to reach the desired degree of tenderness. To expeditetransfer of the bath temperature throughout larger cuts of meat, one caninsert one or more heat conductors, for example aluminum spike(s), inthe meat, taking care that they are inserted in a manner that will notcause perforation of any envelope around the meat.

According to a process of the invention, the entire volume of the bathis maintained at a controlled temperature within a range that hastensenzymatic tenderizing of the particular meat below a minimum cookedtemperature of the meat. Thus in this preferred embodiment, the bathdoes not include even localized areas of liquid at or above the minimumcooked temperature. In embodiments, the process comprises immersing orspraying the meat in or with liquid or a liquid vapor such as steam at afirst temperature within a range that quickly kills surface bacteriawithout substantially cooking the surface of the meat. The meat is thenmaintained in a liquid bath at a second temperature lower than the firsttemperature within a range that hastens enzymatic tenderizing of themeat.

According to a preferred process of the present invention, the entirevolume of the bath is maintained at a controlled temperature within arange of ±2° F. The process of the invention preferably comprisesimmersing food product in a liquid bath and maintaining the bath withina very closely controlled temperature range, for example by heatinglaterally adjacent zones of the fluid and vertically perturbating thefluid, such as with a liquid jet or with bubbles. A suitablethermalizing apparatus for heat treating food product according to thepresent invention including maintaining the bath tempera- ture byheating laterally adjacent zones of fluid and vertically perturbatingthe fluid with bubbles is disclosed in U.S. Pat. No. 5,445,062 toPolster entitled “Rethermalizer.” The entire disclosure of this PatentApplication is incorporated herein by reference.

The rethermalizer is a food heating vessel having sides and a bottom forretaining an aqueous bath, and including heat supply for heating thebath. A food locator rack is positioned in the vessel. The rack has aplurality of defined locations for supporting food product to be heated.Fluid outlets are positioned from the rack to the vessel beneath all ofthe locations to cause fluid to exit into the bath and agitate the bathover and past the food items. A connector connects the rack outlets to apressurized source of fluid. The rethermalizer includes fluid conductingtubes with outlets on the locator rack and upwardly diagonally orientedconduits to conduct pressurized fluid to cause bath circulation. Theheat supply is a heater element embedded in rubber-type material, forexample silicone polymer, bonded to outside of the vessel. The heaterelement can be an electric resistance heater coil embedded betweenlayers of the rubber-type material.

The rethermalizer includes water supply means for supplying additionalwater to the vessel to replace water lost by evaporation and removalwith food product. Sensing elements are spaced at different verticallocations of the vessel with an upper one at the level desired for thebath and a lower one below that level for detecting the differentialsensed by the elements. The sensing elements are operably associatedwith the water supply means for periodically actuating the water supplymeans to add supplemental water to the vessel when a predetermineddifferential is detected. The rethermalizer can include a graphiccontrol panel with the panel having controls and indicators for each offood support locations.

The housing for the rethermalizer can define a heating chamber and aseparate control chamber. The food heating vessel is in the heatingchamber and electronic controls are located in the control chamber. Twowalls between the chambers are spaced from each other and define avertically elongated space. One of the walls is a wall of the heatingchamber and the other wall is a wall of the control chamber. Air inletopenings at the bottom of the space provide for inlet air flow. Airoutlet openings at the top of the space permit outlet air flow into theheating chamber. Heat from the heating chamber createsthermally-generated, upward air flow through the space to isolate andcool the control chamber wall.

Precise temperature control is critical to high quality results incooking and rethermalizing vacuum package foods. Precise temperaturecontrol is also important to the process of heating food product forpasteurizing proteinaceous food product without destruction offunctionality and/or for enzymatic tenderization of proteinaceous foodproduct without substantial cooking according to the present invention.

Heating water or other liquid baths can result in localized too high ortoo low temperatures throughout the bath that impair food productquality. A stirred liquid bath does not flow evenly over all surfaces,but rather takes a path of least resistance. A liquid bath tends tostratify into thermal layers of different temperatures. Even if heat isapplied throughout the surface of a vessel, loading of product into thevessel will cause sometimes widely varying temperature zones to occur.These conditions will prevent accurate temperature control in a hotliquid bath. Inaccurate temperature control within a bath can adverselyaffect the heat treating of proteinaceous food product. Localized hotspots can cause portions of a shell egg to lose functionality throughcoagulation or the like and can cause portions of a tenderizing meat tocook. Low temperature zones can result in inadequate pasteurization ortenderization. Low temperature zones can prevent or reduce tenderizingand even enhance bacteria growth.

The present invention includes both batch and continuous heat treatingprocesses. Temperature control in a liquid is more difficult in acontinuous heat treating process. Liquid is lost from the bath not onlyby evaporation, but additionally by significant liquid transfer withproduct as pasteurized and/or tenderized proteinaceous food product isremoved. Liquid is required to be added to a heated bath usually in asignificant quantity by the time bath level decline is discovered by afood worker. Addition of liquid can cause temperature change in the bathwhether heated or cooled liquid is added. This effect, if notcontrolled, can adversely influence a heat treating process. Control canbe accomplished, however, as discussed below.

Another problem with heating in a liquid bath relates to temperaturecontrol techniques. The thermodynamics of a liquid bath create a lagtime between the application of heat energy and the sensing of the sameby a control system and the establishing of a uniform temperaturethroughout a bath in response to the setting. The thermodynamics of theliquid and the lag time may result in “overshoot” of temperature.

Liquid circulation can help to prevent temperature layer stratificationand overshoot. However, circulation according to conventional bathheating methods is insufficient to provide the control necessary forpasteurization and/or tenderization. Additionally, circulation alonedoes not assure even flow over all surfaces of food product. The foodproduct itself may disturb the circulation pattern of a bath. The bathliquid will take a path of least resistance and may create localizedtemperature zones or layer stratification.

Typical thermostatically controlled liquid baths used for cookingexhibit problems of heating and temperature control as described above.Thermostatically controlled liquid baths are characterized by overshootand localized hot or cold spots. Most thermostatically controlled liquidbaths cannot be used in the process of the present invention to maintainthe entire volume of the liquid bath at a controlled temperature withina range of ±2° F., much less ±1° F. or less.

The Polster rethermalizer is provided with tubes to generate liquidflow. The tubes can inject bubbles, for example air bubbles, or liquidjets at various locations in the vessel to cause scrubbing of surfacesof meat. The resulting action provides excellent heat exchange at meatsurfaces and eliminates temperature zoning and stratification. Thevessel permits an accurate and efficient heat transfer to the meat topermit a uniform temperature within the meat without hot or cold spots.The bubbles or jets cause a vertical perturbation that permits utilizingthe bath for a process of pasteurization and/or tenderizing without bycooking and without undesirable bacteria growth.

The Polster rethermalizer includes specially arranged and cooperativetemperature sensors. The sensors are vertically displaced to providetemperature sensing. Temperature differentials are sensed betweendifferent vertical locations within the bath. The rethermalizer vesselis heated in laterally adjacent zones. A temperature sensor is locatedon the vessel for each zone near the heater to cooperate with sensorsnear the vessel bottom. The arrangement compensates for lag time, i.e.,thermal momentum, and prevents overshoot of temperature above optimumtenderizing temperatures. A vertically displaced set of temperaturesensors permits the addition of water in small regular quantities asneeded to provide level control.

Adding bath liquid at different temperatures within the liquid bath isanother technique that can be used to maintain the liquid bath at acontrolled temperature according to the invention. The process of theinvention can be used for pasteurization, tenderizing or bothpasteurization and tenderizing of proteinaceous food product. Anysuitable thermal conveying liquid may be used as the bath liquid in theprocess of the invention for treating any type of proteinaceous foodproduct. For example, the bath can comprise water or cooking oil.Preferably, the liquid is water. By means of the present process, thetemperature of the bath can be maintained at a temperature ±2° F.,preferably ±1° F. or ±0.75° F. or 0.5° F. Thus the bath can exclude evenlocalized areas of liquid at or above a temperature that impairsfunctionality of or cooks the food product, and/or at or below atemperature at which pasteurization is incomplete to maximize uniformquality of the tenderized meat precut.

The food product can be enveloped in a bag during treatment. Ifenveloped, the bag preferably is made of a relatively non-insulatingmaterial that is substantially impermeable to the liquid of the bath.The material should be impermeable to prevent food product from beingpermeated by the bath liquid. Additionally, the material must berelatively non-insulating to permit transfer of heat from the bath tothe food product. Suitable materials are known to those of ordinaryskill in the art, and can include materials such as those used in manycooking bags and wraps. Appropriate materials for enveloping the foodproduct include polymeric laminates that can be comprised of an oxygenbarrier layer and a moisture barrier layer. The oxygen barrier layer maycomprise a hydrolyzed olefin/vinyl ester copolymer. The oxygen barrierlayer may be a heat-sealable layer comprising high density polyethylene,alone or mixed with polyisobutylene; polypropylene; ethylene-propylenecopolymers; ionomeric resins; polybutene-1 or blends of such polymers.

The laminate may include a substrate layer comprising a polyamide, whichmay be a homopolyamide such as polycaprolactam orpolyhexamethyleneadipamide or a copolyamide; a polyester such aspolyalkylene terephthalate or isophthalate; a polycarbonate;polypropylene; a polyallomer; poly(4-methyl-pentene-1); polybutene-1;polystyrene; polyvinyl chloride; medium or high density polyethylene; anacrylonitrile-butadiene-styrene resin; amethacryonitrile-butadiene-styrene resin or a blend of two or more suchpolymers. Examples of suitable materials are disclosed in U.S. Pat. Nos.3,949,114 to Viola et al., 3,961,086 to Turbak, 3,983,258 to Weaver,3,988,499 to Reynolds, 4,132,048 to Day, 4,136,205 to Quattlebaum and4,534,984 to Kuehne. The entire disclosures of these patents areincorporated herein by reference.

A process according to the present invention for heat treating meat,comprises encasing the food product in a plastic pouch, evacuating airfrom the pouch and sealing the pouch under vacuum. According to apreferred embodiment, the process of tenderizing meat in the absence ofa tenderizing agent (or anti-bacteria agent), comprises vacuum packagingmeat in a pouch, immersing the meat in a liquid bath, and maintainingthe bath at a controlled temperature within a range below a minimumcooked temperature of the meat that hastens enzymatic tenderizing in themeat.

The tenderizing process of the invention is particularly advantageousfor tenderizing meat either in advance of delivery to a serving area orat the serving area immediately prior to cooking. For example,individual steaks can be tenderized in a restaurant by the process.Additionally, the process of immersing a meat in a liquid bath can beconducted at higher temperatures to cook meat. Meat or fish can besubjected to an elevated temperature outside the immersing vessel andfor a brief period of time to provide a grilled appearance or the like.

The pasteurization process of the invention is particularly advantageousfor pasteurizing shell egg and “raw” shellfish because the processprovides a means to precisely control treatment temperature to achievepasteurization without destroying functionality of the food. The egg canbe heated in the range of 134.5 to 139.5° F. for 20 to 345 minutes.Process time can be controlled in ranges from 34 to 52 minutes for apasteurization temperature of 138.9±0.5° F. and up to 75 to 400 minutesfor a pasteurization temperature of 130.3±0.4° F. The process can beused to treat shell egg at an initial temperature of 40 to 70° F. whenthe weight of the egg is 35 to 90 grams and to thereafter heat treat theegg at a temperature of 138±1.5° F. for a total time of 36 to 52minutes. The process can heat treat the egg weighing 50 to 80 grams toan initial temperature in the range of 45 to 55° F. followed by a heattreatment at a temperature of 138±0.75° F. for 39 to 49 minutes.

Times and temperatures for heat treating other proteinaceous productscan be the same as for shell eggs or can be determined by those skilledin the art according to the product treated and the objectives of theheat treatment. For example, pasteurization of seafood may be achievedat the same temperature and time relationships described above for shellegg.

While the invention has been described in connection with specificembodiments, it is to be understood that the embodiments are by way ofillustration and are not intended to limit the invention. For example,while the invention is described in connection with the rethermalizervessel disclosed by Polster in U.S. patent application Ser. No.08/065,627, various sizes of meat may require different size vessels ordifferent types of vessels and various quantities of shell eggs mayrequire different size vessels or different types of vessels. Anenlarged vessel can be utilized to conduct the process of the inventionwith larger cuts of meat or an adapted Polster vessel with a separateheat source for tight control of temperature within the required rangeand/or an outside source of controlled temperature bath liquid can beutilized. An enlarged vessel can be utilized to conduct a process of theinvention for a commercial scale processing of shell egg. While theinvention is described in connection with the rethermalizer vesseldisclosed by Polster and while the invention can be carried out inthermalizer vessels of varying size or Polster thermalizing vessels thatmay be modified, the process of the invention can be conducted by anysuitable apparatus. Additionally, while the focus of the description ofpasteurization has been on the shell egg example, the process applies topasteurization of any proteinaceous food material including by way ofexample, meat and shellfish. In another example, the invention can bemodified to raise the temperature of meat to a pasteurizing ortenderizing temperature and the process can be completed in a conventionenvironment such as in a heated room. In another example, the processcan include a spray bath type of immersion.

What is claimed is:
 1. A process of tenderizing meat in the absence ofan applied tenderizing agent, comprising immersing the meat in a liquidbath liquid and separately heating laterally adjacent zones of said bathliquid to maintain the entire volume of said bath liquid at a controlledtemperature below a minimum cooked temperature of the meat for asufficient time to carry out endogenous enzymatic tenderization of themeat.
 2. The process of claim 1, further comprising verticallyperturbating said bath liquid to disrupt temperature stratification. 3.The process of claim 1, comprising adding liquid to said bath withoutthereby causing greater than 2° F. variations within the entire volumeof the bath liquid.
 4. The process of claim 1, wherein said controlledtemperature is maintained within a range of ±2° F.